This invention relates to a substituted styrene polymer having a plurality of pendant vinylidene groups and also to a graft copolymer derived from said substituted styrene polymer.
As is well-known, the viscosity of a polymer substance is a function of its molecular weight. It is also well-known that branched polymers having star- or comb-like configuration generally have a viscosity lower than straight chain linear polymers having corresponding molecular weights.
Recently, strong demands exist for high-solids coating compositions. In order to achieve this, it is necessary to use low molecular weight vehicle resins so that the resulting coating formulations have a suitable viscosity for application even at high solid contents. However, the use of low molecular weight resins often suffer from certain disadvantages such as decrease in workability and film properties. Since the viscosity of branched polymers is significantly lower than the viscosity of straight chain linear polymers having corresponding molecular weights, their potential as a vehicle resin for formulating high-solids coating compositions is of great interest.
In our Japanese Patent Application No. 239,223, there is disclosed a method for producing a graft copolymer comprising the steps of metallizing poly-(p-methylstyrene)(PPMS) or styrene/p-methylstyrene/styrene ternary block copolymer (SMS) with n-butyl lithium/tetramethylethylenediamine, reacting the resulting pseudogels (precipitates) of metallized polymer with a vinylidene monomer such as 1,1-diphenylethylene (DPE) to form an adduct, and graft-polymerizing acrylic monomers using said adduct as an initiator. This method is advantageous in that the adduct is soluble in conventional inert organic solvents and that undesirable side reactions such as carbonyl addition to the metallized reaction site do not occur.
However, it has been discovered that the resulting product often contains a significant amount of homopolymers of said acrylic monomers. This is because the starting PPMS or SMS is not fully metallized and thus remaining unreacted metallizing agent serves as an initiator of the homopolymerization of acrylic monomers. This side reaction may be avoided by thoroughly washing the metallized polymer with an organic solvent before reacting with the vinylidene monomer to remove unreacted metallizing agent.
It would be desirable for the synthesis of a graft copolymer by the anion polymerization technique to have a metallized polymer initiator which is soluble in a variety of innert organic solvents and which has a high metallizing efficiency (preferably as nearly as 100%) and a high initiator capability. It is also desirable for the graft polymerization to be a living polymerization.
The present invention concerns the provision of a substituted styrene polymer which may give a metallized polymer initiator having the above-described characteristics. The invention also concern the provision of a new graft copolymer having a plurality of side chains grafted to said substituted styrene polymer.